1. Field of the Invention
The present invention relates to an engine starting apparatus for vehicles, and more particularly to an apparatus which assures quiet engine starting with comparatively short engine starting period.
2. Related Art
In a conventional engine starting apparatus for vehicles, a starter motor for cranking a vehicle-mounted engine is energized when an ignition switch is turned on and deenergized when a rotational speed of the engine attains a predetermined speed.
In another conventional engine starting apparatus for vehicles such as disclosed in JP-A-2-97300, an electric generator/motor is used to perform a motor operation for cranking an engine and thereafter switched to perform a power generator operation. During the power generation operation, exciting current to the generator/motor for power generation is kept to a minimum value until the engine is warmed up so that the engine is prevented from stalling.
In the above-described engine starting or cranking operation, it is desired to crank the engine with as large torque as possible to speedily start the engine by overcoming its large load resistance including static friction at the time of initial period of engine starting.
In the last period of engine starting after the engine is started to rotate, the engine starts to produce a driving torque and frictions at various friction surfaces in the engine changes from the static one to the dynamic one to reduce the load resistance. As a result, the rotational speed of the engine increases rapidly and large vibrations and noises are generated, thus degrading quietness and durability of the engine.
Further, applying a large torque from the generator/motor to the engine to rapidly increase its rotational speed after the starting of engine rotation causes unnecessary consumption of electric power in a vehicle-mounted storage battery.